The present invention relates to devices for sensing current in a conductor and, more particularly, to a split core current sensing transformer having core portions which self-align during assembly.
Allocation of power cost among members of a group of users, protection of circuits from overload and/or monitoring continued operation and/or malfunctioning of a remote circuit or device are just a few exemplary reasons for monitoring the flow of electric current in a conductor. Current monitoring is frequently performed with a sensing or current transformer (CT), typically comprising a coil of wire wrapped around the cross-section of a magnetically permeable core which, in turn, encircles a conductor in which the current is to be measured. An alternating current flowing in the conductor, the primary winding of the transformer, magnetizes the core inducing a current in the coil of wire, the secondary winding, which is substantially proportional to the current in the conductor and the ratio of the number of coils in the transformer's primary winding to the number of coils in the secondary winding.
Sensing transformers may have either a solid core or a split core. A solid core is typically a toroid of magnetically permeable material which encircles the conductor in which the current will be sensed. A disadvantage of a solid core sensing transformer is the requirement that the conductor be disconnected when installing the encircling toroidal core on the conductor. Where the conductor to be monitored has already been connected, a sensing transformer with a split core is often used to facilitate installation. Cota, U.S. Pat. No. 5,502,374, discloses a split core transformer comprising a pair of hinged housing halves each enclosing half of a toroidal transformer core. The transformer can be installed on a conductor by pivoting the free ends of the housing/core portions away from each other; positioning the conductor to be monitored in the center of one of the portions; and closing and latching the core halves around the conductor. Bernklau, U.S. Patent Publication No. 2009/0115403, discloses another split core transformer comprising hinged C-shaped or U-shaped transformer core portions. While a hinged split core transformer can be installed without disconnecting the conductor in which the current is to be monitored, sensing transformers are commonly installed in enclosures, such as, a motor starter enclosure, where there is insufficient room to open the hinged portions and maneuver the conductor into position. Bruno, U.S. Pat. No. 7,312,686, discloses a split core current transformer comprising separable core portions. While the disassembled transformer requires no more space than the assembled transformer, it can be difficult to align the core portions when reassembling the core, particularly, in the crowded confines of an enclosure for electrical equipment.
What is desired, therefore, is a split core sensing transformer including core portions which can be conveniently assembled in a limited or crowded space.